The present invention relates to laser irradiation of silicon films. More particularly, it relates to the laser irradiation of an oxygenated, doped, non-single crystalline silicon film.
Silicon films can be characterized by their crystallographic structure and by the type and concentration of impurity atoms they contain. The structures can be classified as crystalline, polycrystalline and amorphous, and the silicon films can be doped with oxygen, hydrogen or typical N or P type conductivity modifiers. A large number of combinations of crystal structure, impurity type and impurity concentration are therefore possible. By manipulating these combinations, it is possible to create a silicon film having electrical properties within a wide range of values. Generally, the conductivity of a silicon film increases as the degree of its crystallinity increases and as the doping concentration of N or P type conductivity modifiers increases. Compared to polycrystalline silicon films, amorphous silicon films tend to be more insulating and single crystalline films tend to be more conducting. As described herein, materials having resistivities greater than approximately 10.sup.8 ohm-centimeters will be characterized as insulating and materials having resistivities less than about 10.sup.2 ohm-centimeters will be characterized as conducting.
Polycrystalline silicon films doped with N or P type conductivity modifiers are electrically conductive and are conventionally used as gates, contacts and interconnections in integrated circuit devices. In U.S. Pat. No. 4,198,246, PULSED LASER IRRADIATION FOR REDUCING RESISTIVITY OF A DOPED POLYCRYSTALLINE SILICON FILM, issued Apr. 15, 1980 to C. P. Wu, and in copending U.S. patent application Ser. No. 065,437, LOW RESISTIVITY POLYCRYSTALLINE SILICON FILM, filed Aug. 10, 1979 by C. P. Wu et al now U.S. Pat. No. 4,229,502, it is disclosed that the conductivity of N or P type polycrystalline silicon films can be further increased by subjecting them to thermal annealing or laser irradiation.
In contrast, oxygenated, polycrystalline silicon films are typically highly resistive and are conventionally used as insulating and passivating layers. Oxygenated polycrystalline silicon, hereinafter referred to as SIPOS, is an insulating material, although its conductivity can be increased if it is doped with an N or P type conductivity modifier. The resistivity of doped or undoped SIPOS can be further manipulated by varying its oxygen concentration, as is described in U.S. Pat. No. 4,014,037, SEMICONDUCTOR DEVICE, issued Mar. 22, 1977 to T. Matsushita and in U.S. Pat. No. 4,086,613, SEMICONDUCTOR DEVICE HAVING A PASSIVATED SURFACE AND METHOD OF MANUFACTURING THE DEVICE, issued Apr. 25, 1978 to J. P. H. Biet et al. The resistivity of pure (nonoxygenated) polycrystalline silicon is approximately 3.times.10.sup.6 ohm-centimeters, whereas SIPOS containing approximately 20 atomic percent oxygen has a resistivity of approximately 10.sup.11 ohm-centimeters. Oxygenated, amorphous silicon is also substantially insulating, typically having a resistivity greater than 10.sup.8 ohm-centimeters.